The red flowering gum (Corymbia ficifolia) is one of the world’s most spectacular trees when in full bloom and in recent times the development of more compact cultivars that are propagated vegetatively (usually by grafting) has made this an even more popular choice as a feature tree for the garden.
Pruning a young plant
When you first plant a flowering gum it is a vital time to shape it according to your design tastes. If, for instance you would like a compact ball-shaped specimen with maximum flowering then you should choose one of the more compact grafted cultivars that are available, especially from specialist native plant nurseries. Tip prune your new plant every couple of months through spring, summer and autumn for the first year after planting and you will develop a dense framework of shoots that will usually produce a more prolific flowering display the following summer.
An exception to this approach is if you want to develop a taller tree with a clean trunk to go at the back of a garden bed. In this case you will want to prune off any lower shoots and leave the strongest shoot to grow at the top of the plant. In my experience, however, most people want to keep their trees compact and as low as possible so it really comes down to what you wish to achieve with regard to the shape of your tree.
Pruning after flowering
The most critical pruning operation with your flowering gum once it is established is to prune it as soon as possible after it finishes flowering. A series of physiological changes happen during and after flowering if the tree is left to its own devices. The first is that the plant starts to put a lot of energy into the formation of the gumnuts, and if this process goes too far it seems to inhibit the production of flower buds for the following year. The second thing is that the tree kicks into vegetative growth that comes from the buds directly behind the spent flowers, and this means that the tree will just get taller and taller if it left to its own devices.
The bottom line is that it is extremely beneficial to prune as soon as possible after flowering to give you the best possible chance of a good flower display the following year. My preference is to prune the tree in such a way as to ensure there are lots of flowers at eye level as well as at the top of the tree (depending on the mature height of the cultivar in question). This can mean reducing the tree by 30% or more in height each year depending on your growing conditions. A set of heavy duty loppers can be a very handy tool as flowering gums are capable of considerable growth in a single year.
When pruning behind the flowers, ensure that you take each back to just above a node, preferably one where a small shoot has already emerged. Generally, these small shoots will kick into growth straight away and provide the flowering branches for the next blooming the following summer. This is also a great time to feed the plant to help ensure good growth straight away that will set up the framework for the next flowering. Even though flowering gums are not particularly sensitive to phosphorus I still use a low P fertiliser in my garden to ensure that any phosphorus sensitive plants such as banksias and grevilleas are not compromised.
Maintenance of the rootstock on grafted trees
The vast majority of flowering gum cultivars are grafted plants so it is well worth checking the graft union at the bottom of the plant. If there are any new shoots emerging from the base of the plant these should be removed while you are pruning the top of the plant. If they are left to grow they will tend to swamp the growth of the scion that is grafted on top that you are wanting to encourage.